Photographic image amplifying with copper ions

ABSTRACT

THIS DISCLOSURE RELATES TO PHOTOGRAPHIC AMPLIFYING SYSTEMS COMPRISED OF A SOLUTION OF COPPER IONS AND CERTAIN REDUCING AGENTS WHICH SELECTIVELY DEPOSIT COPPER COPPER METAL ON LATENT METAL PHOTOGRAPHIC IMAGES TO INCREASE THE DENSITY OF THE IMAGES. THE AMPLIFYING SYSTEMS ARE PARTICULARLY EFFECTIVE WITH LATENT METAL IMAGES OF PHOTOGRAPHIC MEDIA COMPRISING A RADIATION ACTIVATED PHOTOCONDUCTOR. ALSO DESCRIBED ARE PROCESSES FOR AMPLIFYING PHOTOGRAPHIC IMAGES.

United States Patent 3,674,489 PHOTOGRAPHIC IMAGE AMPLIFYING WITH COPPER IONS John E. Wyman, Lexington, Mass., assignor to Itek Corporation, Lexington, Mass. No Drawing. Filed July 11, 1968, Ser. No. 743,981 Int. Cl. G03c 5/24 U.S. Cl. 96-48 27 Claims ABSTRACT OF THE DISCLOSURE This disclosure relates to photographic amplifying systems comprised of a solution of copper ions and certain reducing agents which selectively deposit copper metal on latent metal photographic images to increase the density of the images. The amplifying systems are particularly effective with latent metal images of photographic media comprising a radiation activated photoconductor. Also described are processes for amplifying photographic images.

BACKGROUND OF THE INVENTION (9.) Field of invention This invention relates to processes and systems for amplifying photographic images.

(b) Description of the prior art The intensification, i.e. amplification, of latent metal images in the photographic art has long been known and is described in the literature. Metal intensification systems, including those containing copper ion solutions as the source of intensifying metal, have been described in the literature. In general, metal intensifying systems are electroless plating baths from which the reduced metal is plated out rapidly and selectively on a latent metal image. To be effective, an intensifying system must plate the metal on the latent metal image, i.e. the primary metal image, at a rate substantially faster than on the background of the image. It is obvious then that all electroless plating baths cannot be expected to function as intensifying systems.

Intensification of photographic latent metal images has been described at great length with respect to systems based on silver ion which is most commonly used. The use of copper ion in photographic image intensification has been suggested but operable systems based on copper ions have been difiicult to perfect. The basic problem with copper ion systems has been the need for reducing agents which achieve the necessary selectivity of deposition of copper metal in the latent metal image at a rapid rate to ensure deposition of copper in gray to black form rather than the usual reddish yellow tone which is characteristic of electrolytically deposited copper.

In commonly owned U.S. Pat. No. 3,512,972 is described a successful photographic intensifying system utilizing copper ions as the source of copper metal and, as reducing agent, ascorbic acid. The use of the said system gives excellent results in latent metal image intensification.

The use of photographic media comprising radiationactivatable photoconductors for production of reversible latent images is described in British specification 1,043,- 250. In the patent, the method generally requires the formation on the media of a latent reversible image corresponding to a pattern of activating light, which image can be rendered irreversible by treatment with a redox system which deposits substances in the radiation-struck portions of the media, the deposited substances generally being the reduction product of the reducible component of the redox system. The extent of reduction can be conice trolled to produce an irreversible latent image which is visible or invisible but which can be intensified by exposure to additional amounts of the selected redox system. For example, when the reversible latent image is contacted with silver ions in the presence of a reducing agent for silver ions, e.g. hydroquinone or equivalent reducing agent, the irreversible image obtained is either fully or partly visible, or alternatively invisible, depending on the amount of silver ions used and the activity of the reducing agent, as recognized by those skilled in the art.

The major consideration in attempting to develop suitable intensifying systems with copper ion as the reducible component is to reduce the overall cost of silver salts with relatively inexpensive copper salts, or at least reduce the requirements for silver salts in processing exposed photographic media of the type described.

SUMMARY OF THE HQVENTION There have now been discovered photographic image amplification systems comprising a solution of copper ions and a solution of a reducing agent selected from the group consisting of 'vanadous ion, titanous ion, and complexes of vanadous, titanous or ferrous ion with a complexing organic carboxylic acid containing at least one amino nitrogen and at least two carboxyl groups, said carboxyl groups being separated from said amino nitrogen by at least one methylene or methine group. Preferred com plexes are those formed with such complexing acids in which the amino nitrogen is a tertiary amino nitrogen, e.g. ethylenediaminetetraacetic acid and nitriloacetic acid, e.g. ferrous ethylenediaminetetraacetic acid (FeEDTA), titanous ethylenediaminetetraacetic acid (TiEDTA), titanous nitrilotriacetic acid (TiNfIA), which at present appear to give the best results. complexing agents falling within the ambit of the present invention include the following:

N-hydroxyethylethylenediaminetriacetic acid Diethylenetriaminepentaacetic acid N-hydroxyethyliminodiacetic acid N,.N-ethylenediaminediacetic acid N,N'-dihydroxyethylenediaminediacetic acid 1,2-diaminocyclohexanetetraacetic acid Additional compound useful as complexing agents are hydroxyalkylaminoacetic acids described in U.S. Pat. 2,996,408. Such compounds may contain substituents which do not adversely affect the complexing properties, such as hydrocarbon or substituted hydrocarbon radicals, e.g. lower alkyl groups such as methyl and ethyl in the ethylene radical. The ethylene radical can be replaced with alkylene radicals such as propylene, butylene and the like without altering the complexing property.

The specified reducing agents provide excellent results in the amplification of latent metal images, i.e. primary metal images, of such metals as silver, gold, copper, tin, mercury or palladium. For the purpose of this disclosure, the expression latent metal image is intended to embrace invisible metal images as well as partly visible metal images, as is generally understood by those skilled in the art.

The latent metal image is produced by exposure of a medium comprising a radiation-activatable photoconductor to an image pattern of activating radiation after which the medium is contacted with a solution of metal ions to form the primary metal image, e.g. silver ions. The latent metal image is thus formed and, after removal of excess treating solutions, the latent metal image is amplified with the present new systems. Amplification is accomplished, in general, by contacting the latent metal image with a solution of copper ions and then with the reducing agent solution to obtain the amplified photographic image. If desired, the latent metal image can be contacted with a reducing agent for the selected metal ions to render the latent image at least partially visible.

Where the primary metal image is copper metal, the primary image can be preformed or, alternatively, the primary image as Well as the amplified image can be formed in one processing operation. For example, the photoexposed medium can be immersed in a suitable solution of copper ions and then contacted with the solution of reducing agent, thus giving an all copper image, this embodiment thus obviating the need for any silver ion in production of visible images on the present photographic media.

Optimum results are obtained when the reducing agent is titanous ethylenediaminetetraacetic acid or titanous nitrilotriacetic acid, which appear to provide the most versatile system.

DESCRIPTION OF PREFERRED EMBODIMENTS The photoconductor or photocatalyst is not limited to any group of compounds but may include both organic and inorganic photosensitive materials. Preferred photoconductors useful in this invention are metal containing photocondnctors. A preferred group of such photosensitive materials are the inorganic materials such as compounds of a metal and a non-metallic element of Group VI-A of the periodic table such as metal oxides, such as zinc oxide, titanium dioxide, zirconium dioxide, germanium dioxide, indium trioxide, tin oxide, barium titanate; metal sulfides such as cadmium sulfide, Zinc sulfide and tin disulfide; metal selenides such as cadmium selenide. Metal oxides are especially preferred photoconductors of this group. Titanium dioxide is a preferred metal oxide because of its unexpectedly good results. Titanium dioxide having an average particle size less than about 250 millimicrons and which has been treated in an oxidizing atmosphere at a temperature above about 200 C. is especially preferred, and more especially, that titanium dioxide produced by high temperature pyrolysis of titanium halide.

Also useful in this invention as photoconductors are certain fluorescent materials. Such materials include, for example, compounds such as silver activated zinc sulfide and zinc activated zinc oxide.

Organic photoconductors suitable for use in this invention are, for example, the imidazolidinones, the irnidazolidinethiones, the tetraarylazacyclooctatetraenes, and thiazines, such as l,3-diphenyl-4,5-bis(p-methoxyphenyl) imidazolidinone-Z; 4,5 bis(para-methoxyphenyl)imidazo- Iidinone 2; 4 phenyl 5 (para-dimethylaminophenyl) imidazolidinone-Z; 4,5-bis(para-methoxyphenyl)imidazolidenthione 2; 3,4,7,8 tetraphenyl l,3,5,6-tetraaza cyclooctatetraene 2,3,6,8.

While the exact mechanism by which the media are activated is not known, it is believed that the exposure to activating light, e.g. ultraviolet light, causes the transference of electrons of the photoconductor from the valence band to the conductance band, or at least to some similar excited state whereby the electron is loosely held, thereby converting the photoconductor from an inactive to an active form. If the photoconductor in the active form is in the presence of an electron-accepting agent, a transfer of electrons will take place between the photoconductor and the electron-accepting agent and the latter will be reduced. Accordingly, a simple test to determine whether photoconductors have reducing properties is to mix the material in question with aqueous silver nitrate. In the absence of light, little, if any, reduction of silver ions should occur. At the same time as exposing the same mixture to light, a control sample of an aqueous silver nitrate solution alone is similarly exposed, and if the mixture darkens faster than the control sample, the test material is a photoconductor with reducing properties.

*Periodic Table from Lange's Handbook of Chemistry, 0th edition, pp. 56-57, 1956.

It is evident that the gap between the valence and the conducting band of a compound determines the energy needed to make electron transitions and the light required to provide the needed energy is called bandgap light, as employed herein. The higher energy needed, the higher the frequency to which the photoconductor will respond. It is known in the art that electrons may be present in secondary levels within the band gap due to impurities or defects in the structure of the photoconductor. With light of suitable energy, which in this case would be less than the band gap, electrons from these levels could be raised to the conduction band. A typical example of a secondary level due to a defect in the structure would be an F-center (electrons trapped at negative ion vacancies in an alkali halide crystal). The band gap of KCl is about 8.5 ev. (1460 A.), but the secondary levels due to F- centers are about 2.4 ev. (5400 A.) below the conduction band. Electrons could be raised to the conduction band with 5400 A. light. An example of an impurity photoconductivity could be ZnS doped with Cu. The band gap of ZnS is about 3.7 ev. (3350 A.), but by doping it with Cu one could introduce some secondary levels which would result in photocondutcion due to 4600 A. light.

The photoconductors of this invention may be sensitized to visible and other wavelengths of light by foreign ion doping, addition of fluorescent materials, exposure to radiant energy to elevate the electrons to levels between the valence band and the conduction band and/or by means of sensitizing dyes. Bleachable dyes useful for sensitizing, the photoconductors of this invention include, for example, the cyanine dyes, the dicarbocyanine dyes, the carbocyanine dyes, and the hemicyanine dyes such as disclosed in commonly assigned copending U.S, application Ser. No. 633,689 filed Apr. 26, 1967.

As is generally known, the activation of photoconductors, i.e. transference of electrons from valence bands to conductance bands, is not permanent but rather the activation decays primarily as a function of time. The decay is apparently due to the loss of electrons in the conductance bands, the electrons reverting to lower energy levels, many reverting to the original valence band and others to energy levels intermediate between the respective bands, i.e. secondary levels, or traps. After decay of the activated photoconductor, the medium retains little, if any, ability to reduce silver ions, or similar metal ion, due to the fact that there are little, if any, elecrons in the conductance band. Accordingly, if the medium while activated is contacted with a liquid redox system, reduction of the reducible component thereof occurs. If the reducible component, in the reduced form, is a particulate solid, the result obtained is a visible image corresponding to the pattern.

The foregoing theoretical explanation is offered to enable a better understanding of, and is believed to reasonably interpret, the photoconduction phenomenon of this invention. Of course, the applicants are not necessarily bound by this explanation.

The medium comprising the photoconductor can be an inert carrier sheet which is usually any suitable backing of sufficient strength and durability to satisfactorily serve as a reproduction carrier. The carrier sheet may be in any form, such as, for example, sheets, ribbons, rolls, etc. The sheet can be made of any of a variety of suitable materials such as wood, rag content paper, pulp paper, plastics such as polyethylene terephthalate (Mylar) and cellulose acetate cloth, metallic foil and glass. The preferred form of the carrier sheet is a thin sheet which is flexible and durable.

It is also useful to use a binder agent to bind the photosensitive materials to the carrier sheet. In general, these binders are translucent or transparent so as not to intrefere with transmission of light therethrough. Preferred binder materials are organic materials such as resins. Examples of suitable resins are butadiene-styrene copolymer, poly(alkyl acrylate) such as poly-(methacrylate),

polyamides, polyvinyl acetate, polyvinyl alcohol and polyvinylpyrrolidone.

The photoconductor should be conditioned in the dark before exposure. Such conditioning is generally conducted from one to twenty-four hours. After conditioning, the photoconductor is not exposed to light prior to its exposure to activating radiation for recording an image pattern.

This period of exposure will depend upon the intensity of the light source, the particular imaging material, particular photoconductor, the type and amount of catalyst, if any, and like factors known to the art. In general, however, the exposure may vary from photo-flash to up to several minutes.

The latent metal image formation is accomplished by contacting the activated medium with a redox system composed of an oxidizing agent optionally containing a reducing agent. The oxidizing agent is usually silver ions, but also includes such metal ions as mercury, copper, gold, tin or palladium ions and thus is the image-forming component of the image-forming material. The reducing agent of the redox system can be any of the known reducing agents for the oxidizing agent which are compatible with the present media and systems. For example, the reducing agents include organic compounds such as oxalates, formates, substituted and unsubstituted hydroxylarnine, sub stituted and unsubstituted hydrazine, ascorbic acid, aminophenols, diamines and dihydric phenols. Specific suitable reducing agents include hydroquinone, oand p-aminophenol, p-methylaminophenol, p-hydroxyphenylglycine, oand p-phenylenediamine and l-phenyl-3-pyrazolidone. The formation of the latent image is a function of the concentration of oxidizing agent, i.e. metal ion, and, if used, the activity of the reducing agent. The more facile method of controlling the extent of latent metal image is by controlling the quantity of metal ion in the medium prior to reaction with the reducing agent. Such considerations are well within the skill of the art and should not require excessive explanation herein. It should suffice for the purpose of this disclosure to indicate that the procedure for preparing the latent metal images is accomplished by controlling the amount of metal ion in the photographic medium by exposing to extremely dilute solutions of the metal ion or controlling the length of time of immersion of the medium in a solution of metal ion of higher concentration. Although either procedure can be used with equal effectiveness, it is preferred to utilize dilute solutions of the metal ion, particularly where the metal is silver, in view of economic considerations. As is obvious to any one in the art, the metal ion can be provided in the form of a soluble compound of the metal which does not adversely affect the desired effect. For example, silver ion is provided by dissolving silver nitrate in water or methanol.

The exposed photographic medium once sensitized with the oxidizing agent, i.e. metal ion, can then be treated with the reducing agent, e.g. in solution which is generally stabilized to permit longer shelf-life. The most commonly used stabilizer is sodium sulfite although many other stabilizers are available and known to those skilled in photographic processing. This treatment is by the standard methods and does not require any special methods beyond those normally exercised in routine photographic processing. Optimum conditions for this step are easily determinable and are dependant on the selected reducing agent and the specific metal ion. When using silver ion as the oxidizing agent, p-methylaminophenol is the preferred reducing agent since it appears to give the best overall results and the reducing conditions are quite compatible with the remaining processing steps, i.e. the image intensification or amplification with copper.

Before proceeding with the image intensification, it is usually desirable, but not always essential, to fix the media to remove traces of metal ion which would be reduced in the subsequent processing steps. If the initial metal ion solution is sufficiently dilute, the fixing step is not always necessary. When significant amounts of the metal ion are present in the media, however, they should be removed by any of the art-recognized methods. For example, when the metal ion is silver, the preferred metal at present, a solubilizing agent can be used. Usually, the most facile method entails the use of agents which form soluble complexes with silver ion, such as thiosulfate or thiocyanate ion, the former being preferred under most circumstances. In lieu of a separate fixing step, the solubilizing agent, e.g. thiosulfate ion, can be incorporated into the subsequent treatment solution, e.g. the copper ion-containing solution, or even in the copper ion-developer solution, or in both solutions, as desired.

The image intensifying systems of the present invention comprise a solution of copper ions and a solution of the indicated reducing agent. The copper ion solution may be comprised of copper I or copper II ions. For copper II ion solutions, any of a variety of soluble copper II, i.e. cupric, compounds can be employed. Suitable compounds include various soluble copper salts such as the nitrate, sulfate, acetate, chloride and the like. When cupric chloride is the source of cupric ions, it is preferred to utilize excess chloride ions to minimize, if not completely prevent, precipitation of cuprous chloride during the subsequent reduction step.

For copper I, i.e. cuprous, ion solutions, it is somewhat difiicult to prepare simple solutions in view of the limited solubility of cuprous compounds. For example, cuprous halides are not very soluble. However, the cuprous compounds can be very readily solubilized by formation of complexes which is a wellknown property of cuprous ion. For example, cuprous chloride is readily solubilized in the presence of excess chloride ion or thiosulfate ion. Alternatively, insoluble cuprous com pounds can also be solubilized by reaction with complexing molecules such as ammonia. However, when ammonia is employed, the resulting solution is extremely sensitive to oxidizing conditions and care has to be exercised therefore. Of course, the oxidized form of cuprous ion is cupric ion which is equally effective in the present systems. As with cuprous ion, cupric ion forms similar complex ions in which form it is also useful in the present intensifying system.

Particularly effective complexes of copper ions are the complexes formed with nitrilotriacetic acid and ethylenediaminetetraacetic acid, especially when used with TiNTA or TiEDTA as reducing agent. These combinations give excellent results for which reason they are preferred.

As will be fully appreciated, the concentration of cupric ion in the solution is not excessively critical. A minimum of routine experimentation will indicate the optimum concentration of copper ion for any given system. Usually, the concentration will be found in the range from about 0.1 M to about 1.0 M, and preferably from about 0.25 M to about 0.6 M, although other concentrations can also be used but without any appreciable benefit, and possibly with some difiiculty, particularly with more concentrated solutions.

The solution of reducing agent is prepared by dissolving the reducing agent in a suitable solvent, which, for practical purposes, is normally an aqueous solvent sys: tem, and usually water to which may be added other compatible solvents such as lower alkanols. For most purposes, water suffices as solvent and is preferred. The addition of other solvents compatible with the present system is generally avoided but tolerable within practical limits as should be obvious to anyone skilled in the art. More conveniently, the reducing agent, when a complex compound, can be formed in solution by addition of a common soluble salt of the metal ion thereof and the complexing agent, preferably in the form of a salt. For example, FeEDTA is conveniently formed by dissolving a suitable ferrous salt and tetrasodium ethylenediaminetetraacetic acid, Na EDTA. Similarly, TiNTA is formed in solution by addition of a titanous salt to a solution of trisodium nitrilotriacetic acid, Na NTA. As an alternative, though it does not provide any appreciable advantage, the specific reducing agents can be formed in solution at supersaturation concentration and the precipitated reducing agent separated, e.g. by filtration or centrifugation, employing standard recognized techniques. The specific reducing agent can then be dissolved to form a solution of desired concentration. When the reducing agent is formed by the preferred method, care should be exercised in selecting the source of the necessary metal ions and the complex compound to avoid inclusion of substances which would adversely affect the normal function of the reducing agent under the conditions of use.

The concentration of the reducing agent should be sutficient to accomplish the desired reduction of copper ions. For any given system, the optimum concentration can be readily determined by a minimum of experimentation. While a wide range of concentration can be employed, in general, the optimum concentration of reducing agent is in the range of from about 0.1 M to about 0.5 In. As should be obvious to those skilled in the art, the concentration of reducing agent is not critical, except as a matter of efficiency of operation and the time requirements of any processing sequence. The aforementioned preferred range of concentration appears to give the most desirable results from the viewpoint of effective image amplification in relatively short periods of time. For example, when amplifying a latent silver image with cupric ion, the aforementioned preferred concentration results in full amplification within about one minute, generally reaching a maximum within about 30 seconds. Other concentrations are operable with suitable alteration is operating time periods. The reducing agent solution is preferably maintained at neutrality or at acid pH, preferably above 2, although it is operable at pH values above 7. Generally, the preferred pH range is from about 3-6.

As previously mentioned, the solutions of reducing agent and copper ions, respectively, may contain other agents to assist in image intensification and improve formation of an image. The solutions can contain a solubilizing agent for the oxidizing agent, i.e. metal ions, e.g. silver ions, of the initial redox system. The solubilizing agent is preferably thiosulfate ion which gives best results, although the less eificient thiocyanate ion can be employed. Where the reducing agent is readily oxidized, particularly under atmospheric conditions, a preservative, i.e. antioxidant, can be employed. Soluble sulfites or bisulfites, e.g. sodium sulfite or bisulfite, can be added to the reducing agent solution. Vanadous ion when used as reducing agent is particularly susceptible to oxidation under ambient conditions and requires stabilization. One method of stabilization is protecting these reducing agents from contact with atmospheric oxygen by blanketing with a non-reactive gas such as nitrogen or argon.

In general, the intensification system of this invention comprises a two solution system containing copper ions and reducing agent in the respective solutions as previously described. The process of fully developing a photoexposed medium comprising a radiation-activatable photoconductor can be in a three-solution system as follows:

(1) oxidizing agent, eg. silver ion, solution (2) copper ion solution (3) copper ion-reducing agent solution The inclusion of a reducing agent for the oxidizing agent can be effected by provision of a separate solution to be used after solution 1 and before solution 2, or the reducing agent can be included in solution 2. Each of the systems, i.e. 3 solutions and 4 solutions, makes the overall processing eminently suited for automated processing, for example, in automated photographic development apparatus, or in photoduplicating apparatus which utilize copy media as hereindescribed for multiple copying. The three solution system is particularly suited for automated processing, particularly in the production of multiple copies of a master. The three solution system permits the use of a developing system composed on only three treatment stations, i.e. baths, in the automatic processor which has additionally the very desirable advantage of being based on only slight silver requirements, the visible images being predominantly copper. For example, the silver bath can be of a concentration of as little as 0.001 M silver ion and even lower. If copper intensification is not used, the normal requirement of silver ion is at a concentration of about 0.2 M to obtain a black image. The economic advantage of replacing silver in the image formation becomes more apparent when it is realized that one pound of silver nitrate will make about 700 gallons of 0.001 M silver nitrate, but only 3.5 gallons of 0.2 M solution.

The overall processing time is also an outstanding advantage of the present intensification systems, processing times of 1-2 minutes being quite practical with the aforementioned three solution development system.

In another embodiment of the invention, where the visible metal image is all copper, a simple development system is provided by the present intensification systems, since the copper ion solution forms the latent metal image and then intensifies the image to obtain an all copper image. For the formation of the latent copper image, it is preferred to first treat the photoexposed medium with an oxygen-scavenger, i.e. a compound which reacts with oxygen. Although not wishing to be bound by this explanation, it is assumed that oxygen absorbed on the surface of the photoconductor reoxidizes the copper of the latent metal image as it forms and precludes the possibility of obtaining good visible images. Treatment with oxygen scavengers such as hydrazine, sulfite ion, the ferrous salt of ethylenediaminetetraacetic acid, and the like, permit formation of latent copper images with intensification to visible images of good contrast and density. Triphenylsulfom'um chloride also permits formation of the requisite latent copper image. These agents are preferably used to treat the photoexposed medium prior to contacting with the copper ion solution, but they may be incorporated into the copper ion solution and applied to the photoexposed medium simultaneously. In the latter case, the visible intensified images tend to have a lower density than in the former. The surprising effect of oxygen scavengers on formation of copper latent images is also noted in the formation of latent silver images where similar improvement is obtained.

As an alternative, the latent copper image can be formed by contacting the radiation activated photoconductor with the cupric ion solution as a result of which cuprous ion is formed which then, on heating, disproportionates to form copper metal. The latent copper image can also be formed if copper ion is present in contact with the radiation-activatable photoconductor at the time of exposure to activating radiation. In this latter modification, it is preferred to sensitize the photoconductor by wetting with a solution of copper ions and allowing the solution solvent to evaporate. The photoconductor may be so sensitized either before or after it is coated on the selected substrate.

For the purpose of this disclosure and the appended claims, the foregoing methods of forming a latent copper image are generally referred to as sensitizing with copper ions and the use of such expression is intended to embrace generically the various methods described for forming the copper latent image.

The quality of the intensified image can be controlled as to the blackness of the copper deposit. Urea and thiourea compounds can be added to either the copper ion solution or preferably the reducing agent solution, preferably at a concentration ranging up to 10 M. With thiourea or its derivatives, e.g. ethylenethiourea, the copper deposit is blue black in color. Urea tends to favor a reddish tint to the black deposit, but favorably affected the uniformity of the copper deposit. Combinations of urea and thiourea give the advantages of each and, in proper ratios, the optimum combined benefits are obtained. In a ratio of about 2 moles of urea to about one mole of thiourea, optimum results are obtained with the preferred systems hereinbefore described.

In the foregoing description, and in the following examples, the preferred order of use of the copper ion solution and the reducing agent is the sequence indicated. However, it is possible to first immerse the latent metal image-bearing medium in the reducing agent, followed by the copper ion solution. However, with this reverse order the results obtained may not always be optimum, nor easily reproducible, for which reason, though operable, it is not preferred.

The present amplifying systems can also be used to amplify latent images in photosensitive media other than those containing a photoconductor as the photosensitive component, for example, silver halide emulsion film. Weak latent images can be intensified using the present amplifying systems, in general, using the same procedures hereinbefore described.

The following examples are intended to further illustrate the present invention.

EXAMPLE 1 This example shows the use of a three bath processing system.

A sheet of paper coated with titanium dioxide (as described in British specification 1,043,250) having a particle size of about 30 millimicrons is exposed for seconds on an EG&G Mark 6 sensitometer having an Xenon flash source providing daylight quality radiation to give an exposure of 5000 meter candle seconds. After a 10 second wait, the sheet is immersed in 0.0025 M silver nitrate (aq.) for 10 seconds and drained for 10 seconds. Next the sheet is immersed for 30 seconds in a solution which is 0.3 M CuEDTA and 0.020 M Na S O and contains 2 g./l. p-methylaminophenol and then drained for 10 seconds. The sheet is then developed in a solution of Ti-EUI'A which is about 2.5 10 M in thiourea to obtain a visible image of good density and contrast.

The TiEDTA solution is prepared by adding 10 ml. of titanous chloride solution to a solution of ml. of 1 M Na EDTA in 75 ml. of H 0.

EXAMPLE 2 This example shows the use of a four bath processing system. A titanium dioxide-coated sheet is exposed to a line negative for 3 seconds on a print box and then held for 10 seconds. The sheet is immersed for 10 seconds in 0.001 M aqueous silver nitrate, drained for 10 seconds, developed for seconds in a solution of 2.0 g. p-methylaminophenol and 7.5 g. sodium sulfite per liter and then drained for 10 seconds. The strip is next immersed in 0.35 M CuEDTA and 0.010 M sodium thiosulfate for 30 seconds, drained for 10 seconds, and developed in TiEDTA solution (as in Example 1) for 15 seconds. The strip is then water washed. An excellent copy of the line negative is obtained.

EXAMPLE 3 A photoexposed titanium dioxide-coated paper sheet (exposure=10- sec.) is immersed in 5X10- M silver nitrate for 10 seconds, drained for 10 seconds, and developed in a solution of 2 g. p-methylaminophenol and 7.5 g. of sodium sulfite for 5 seconds. The sheet is fixed for one minute in 0.5 M Na S O containing sodium sulfite (10% by weight based on Na S O The sheet is next rinsed in water for one minute, and then treated with hypo clearing agent (18 g. Na SO and 4.8 g. of

NaHSO per liter) for two minutes. The silver primary image is then amplified by treating with 0.25 M aqueous cupric nitrate for 30 seconds, draining for 10 seconds, and developing with FeEDTA solution for 30 seconds followed by water washing.

The developer solution consists of 50 parts of Na EDTA, 50 parts of IM acetic acid and parts of ferrous ammonium sulfate.

EXAMPLE 4 The procedure of Example 3 is repeated with thiourea in the developer solution at a concentration of 2.5 X 10- M. The image is of a dark blue-black color with very low fog and approximately 5 more steps are gained in the weak silver image which are not visible prior to amplification. When the concentration of thiourea is varied over the range 1.25-3.75 X 10*, similar results are obtained.

The thiourea can also be added to the copper salt solution, but the effect is not as great as in the developer solution.

Similar results are obtained with ethylenethiourea, in lieu of thiourea, at a concentration range of 0.7l.0 10" M. Urea also gives similar results.

The ranges mentioned in this example are those which give optimum results.

EXAMPLE 5 \An FeEDTA developer solution is prepared from 50 parts of IM NagEDTA, 17 parts of 2 M acetic acid, 33 parts water, and 100 parts of 0.5 M ferrous ammonium sulfate with 0.5 part of IM thiourea.

Various concentrations of copper salt solutions are prepared and used in the procedure of Example 3. The concentrations which showed optimum result range from 0.25 M to 0.60 M cupric ion. The amplified images obtained in the said concentration range gave maximum optical densities in the range 1.204.28, with the density of the eleventh step (step wedge) being 0.7-0.8. The fog plus background even at highest concentrations is 0.18- 0.22.

EXAMPLE 6 Titanium dioxide coated sheets of paper are exposed to a line negative on a print box for 2 seconds and held for 10 seconds. The sheets are processed using the following sequences.

Sequence A (1) Immerse for 10 seconds in 0.002 M silver nitrate (aqueous) and drain for 10 seconds.

(2) Immerse for 30 seconds in an aqueous solution of 2.0 g./l. p-methylaminophenol and 7.5 g./l. sodium sulfite. Only a very faint yellow image in the high exposure areas is visible.

(3) Immerse for 30 seconds in 0.35 M CnE'DTA (prepared with CuSO and Na EDTA) which is also 0.04 M Na S O and then drained for 10 seconds.

(4) Develop for 15 seconds in TiEDTA solution (pH=4) as described in previous examples.

A good copy of the line negative is obtained. Elemental analysis of the metal deposit shows it to be about 1.5% silver and 98.5% copper by weight.

Sequence B (1) Immerse in 0.001 M aqueous silver nitrate for 10 seconds and drain for 10 seconds.

(2) Developer as in Sequence A (3) Immerse in 0.30 M CuEDTA (prepared from cupric nitrate) which is 0.01 M Na S O for 30 seconds and drain fro 10 seconds.

(4) Develop in TiEDTA solution (pl-1:4) prepared as previously described and to which is added 0.25 ml. of 1M thiourea solution per ml. of developer to obtain a good print of excellent density and contrast.

The procedure of Sequence B is repeated except that 1 1 the thiosulfate is eliminated from step 3 with little change in the background of the resulting print.

EXAMPLE 7 The procedure of sequence B of Example 6 is repeated using 0.30 M *Cul-EDTA prepared with 50 ml. 1M CuEDTA (prepared with CuSO 250 ml. IM CuEDTA (prepared with cupric nitrate) and 10 ml. of 1M diluted with water to a volume of one liter. The prints obtained are of excellent density and contrast.

EXAMPLE 8 The procedure of Sequence A of Example 6 is repeated using cupric sulfate in lieu of CuEDTA with comparable results.

EXAMPLE 9 A transparent film prepared by coating titanium dioxide in a gelatin binder on cellulose acetate sheet is exposed on a sensitometer for 10 second and sensitized in 0.005 M silver nitrate. Then the film is developed using the silver developer of Example 3, followed by fixing of the silver ion and washing. The film which has a light brown image is immersed in 1M Cu(NO for 30 seconds, drained 10 seconds and then developed for 30 seconds in 0.1 M FeEDTA solution to obtain a dark gray to black image. The film is then rinsed to remove excess developer and cupric nitrate. The film shows ten steps on the stepwedge and no background stain.

As the concentration of the solution of cupric salt increases, there is a tendency for development of a light blue to green stain in the film.

The thus produced imaged film is contacted with a softening bleach bath of the following composition:

1 part of an aqueous 6% H solution combined with 3 parts of the following solution:

Cu-SO -H O: 150 gms. KBr: 4 gms.

Cone. H 80 50 ml. Water to 1500 ml.

The thus bleached film is washed and then contacted with a cyan transfer dye and used as a dye transfer matrix as disclosed in copending U.S. patent application Ser. No. 712,931 filed Mar. 14, 1968.

EXAMPLE A 0.2 M solution of cu-prous chloride which is 0.6 M NH Cl is used in the procedure of Example 9 with comparable results. The copper solution is stabilized with excess sodium sulfite.

EXAMPLE 11 \A copper-amplified image as prepared in Example 9 is immersed for 30 seconds in 0.005 M silver nitrate to plate silver on the copper.

Similarly, immersion in a dilute solution of chlorauric acid (0.008 M) for 30 seconds results in gold plating of the copper image.

The thus plated images are more stable than the copper metal images.

EXAMPLE 12 A titanium dioxide-coated paper soaked in 1 M Cu(NO and dried is exposed on a print box for 2 minutes. The latent image is amplified by immersion in 0.25 M FeEDTA to obtain a heavy dark copper image.

EXAMPLE 13 A titanium dioxide-coated paper is exposed on a Besseler Box for 1 minute, held for 10 seconds, dipped for seconds in 0.1 M mercuric chloride, drained for 10 seconds, immersed for 20 seconds in a solution composed of:

12 30 ml. of l M CuCl in 3 M NaCl 30 ml. of 3 M NaCl 50 ml. of 1 M Na SO and drained for 10 seconds. The paper is then developed for 30 seconds in a solution composed of:

30 ml. of 1 M Na EDTA 30 ml. of 1 M acetic acid 60 ml. of 0.5 M ferrous ammonium sulfate The original weak mercury image is amplified by copper to a black image.

EXAMPLE 14 M1. 2 M Cu Cl 5 M NaCl drained for 10 seconds and developed for 30 seconds in a solution of FeEDTA (prepared from 50 ml. of 1 M Na EDTA, 33 ml. of Water, 17 ml. of 2 M acetic acid and 100 m1. of 0.5 M ferrous ammonium sulfate) followed by water washing.

When urea is added to the cuprous solution, the number of observable steps is increased as well as the uniformity of copper deposit. However, the images show a slight reddish tone. A blue-black color is obtained when thiourea is added to the copper-developer solution. In the system described in this example, the combined optimum results of these additives are obtained when both additives are employed at concentrations obtained with 3 ml. of 1 M urea and 1.5 ml. of IM thiourea in the cuprous and FeEDTA solutions, respectively, in the same amplifying system. The resulting prints have images with 19 steps (stepwedge), a maximum optical density of 1.25, density of the eleventh step of 0.90 and fog plus back ground of 0.19.

EXAMPLE 15 Titanium dioxide-coated paper sheets are exposed on a print box for 15, 30 and 60 seconds respectively. The exposed sheets are immersed for 5 seconds in 0.45 M cupric nitrate containing 1 ml. of 50% aqueous triphenylsulfonium chloride per liter and then developed with FeEDTA solution (as previously described), for .30 seeonds. Dark images (consisting of copper only) are obtained on the sheets, but of lower optical density when compared to the product of Example 16.

EXAMPLE 16 A titanium dioxide-coated paper sheet is exposed for one minute on a print box, held for 10 seconds, immersed in a solution of hydrazine for 30 seconds, drained for 15 seconds, immersed in a 0.45 M solution of cupric nitrate, drained for 10 seconds and then developed with FEEDTA as described in previous examples. An image of good density and contrast is obtained.

EXAMPLE 17 The procedure of Example 16 is repeated using a solution of FeEDTA in lieu of the solution of hydrozine with comparable results.

When the hydrazine treatment of Example 16 or comparable FeEDTA treatment of Example 17 is omitted, reasonably visible images are not obtained by the described procedure.

The all-copper images of Examples 15, 16 and 17 have greater permanence than the silver-copper images of the preceding examples.

13 EXAMPLE 1:;

A commercially available, silver halide-emulsion film is photoexposed and developed using conventional monobath developer and fixer. The dried film shows eight steps and a maximum optical density of 0.37 (fog plus background=0.04). The film is processed by immersion in 0.25 M cupric nitrate for one minute and FeEDTA developer (as previously described). The amplified film shows nine visible steps and a maximum optical density of 0.44.

When a comparably processed film is immersed in a cuprous chloride solution as in Example 14 for 3 minutes and FeEDTA for one minute, the maximum optical density is 0.56, fog level 0.05 and 11 steps are visible.

EXAMPLE 19' The procedure of Example 1 is repeated with TiNTA in lieu of TiEDTA with comparable results. The TiNTA is produced by mixing a solution of titanous chloride and one of trisodium nitriloacetic acid.

When a comparable solution of titanous chloride is used in lieu of TiEDTA solution, similar results are ob tained.

In the foregoing examples, the photosensitive media are principally paper and plastic film coated with the photoconductor. Similar results are obtained with metal foil coated with titanium dioxide, such as aluminum sheets coated with titanium dioxide as described in commonly assigned copending U.S. application Ser. No. 446,707 filed Apr. 8, 1965, now abandoned.

EXAMPLE 20 A brush-grained aluminum plate with a thin photosensitive coating of TiO;,, in a water soluble poly (vinyl alcohol) binder is exposed for 20 seconds through a negative on a cold light print box, held seconds, then immersed in 0.01 M silver nitrate for 10 seconds. The specimen is then immediately dipped into a solution which is 0.2 M in OJEDTA and contains 2 g. Metol and 7.5 g. Na SO for thirty seconds and immediately developed in TiEDTA for seconds. The photo-sensitive coating is then removed by washing in cold water, which also largely removes the image. However, some copper is deposited in an imagewise manner on the brush-grained surface. This image is not in electrical contact with the aluminum as is evidenced by the fact that the copper image is not amplified when the copy medium is placed in a CuEDTA- Na EDTA plating bath.

The brush-grained aluminum oxide coating is penetrated in an imagewise fashion by cycling the above specimen between the CuEDTA bath and the TiEDTA bath, forming a copper image cemented to the aluminum substrate. This copper image is in electrical contact with the aluminum support as is shown by the amplification of this image which occurs when the copy medium is placed in a CuEDTA-Na EDTA plating bath. This plate is then used with an oil base ink on an offset press for making multiple copies.

EXAMPLE 21 A subbed triacetate film or Baryta paper is coated with a solution of ferrous EDTA in a suitable binder and dried in the absence of oxygen. This thus coated substrate is then coated with a slurry of TiO in a suitable binder and dried in the absence of air. The thus prepared copy medium is then exposed imagewise to light, contacted briefly (1-10 seconds) with 1x10 M silver nitrate, then optionally developed in a solution of 2 g. Metol and 7.5 g. Na SO /liter for 1-15 seconds, and finally treated with 0.25-0.75 M cupric nitrate or sulfate for 15-60 seconds. The thus prepared print containing a visible image is then washed and dried.

14 EXAMPLE 22 An anodized aluminum plate is coated with ferrous EDTA in a slightly hardened gelatin binder and dried in the absence of air. This thus coated support is then coated with a Ti0 slurry containing cupric nitrate or cupric sulfate in a suitable water permeable binder and then dried quickly in the absence of air. This thus prepared copy medium is then exposed imagewise to light and immersed directly into a water bath immediately after exposure to produce a visible all copper image adherently bonded to an anodized aluminum plate.

EXAMPLE 23 Titanium dioxide coated sheets are exposed for 3 seconds on a print box, held for 10 seconds, immersed for 10 seconds in m1. of 0.0005 M AgNO which contains 2.5 ml. 1 M NagNTA and drained for 5 seconds. The sheets are then immersed for 15 seconds in 0.3 M CuEDTA (prepared with CuSO and drained for 5 seconds and then developed in TiEDTA developer (described in Example 1) for 5 seconds and finally water washed. The prints obtained are of excellent density.

In addition to amplifying photographic images as described in the foregoing examples, the present systems and processes are also useful in the production of printed circuits as described in commonly assigned copending U.S. applications Ser. Nos. 721,778, filed Apr. 16, 1968 and 717,502 filed Apr. 1, 1968 now abandoned.

In the foregoing disclosure and in the attached claims, reference to the various metal complexes by use of conventional abbreviations, e.g. TiEDTA, TiNTA and CuEDTA, is intended to denote the complex ion made up of the indicated metal ion and an ion corresponding to the indicated acid. As is obvious to anyone skilled in the art, the stoichiometry of the complexes is not necessarily a simple 1:1 ratio but may vary somewhat according to the relative concentrations of the respective ions in solution. Since these complexes are formed readily from relatively soluble sources of the respective ions in solution and the additional ions of these sources in the solution do not adversely affect the formation of the desired complex, nor are they appreciably reactive in the oxidationreduction reactions involving the desired complex, there is no need to designate the additional ions when referring to the complex. Of course, the additional ions are those remaining in solution and not involved in the complex formation, e.g. alkali metal ions, such as sodium or potassium ions, or ammonium ion from the source of complexing acid, and the negative ion of the metal salt introduced, e.g. sulfate, nitrate, halide and the like. Thus, the designation of the complexes by such expressions as titanous nitrilotriacetic acid, ferrous ethylenediaminetetraacetic acid and the like is intended to embrace the complex ions in soluton, irrespectve of the source of the respective ions which make up the complex. As anyone skilled in the art will appreciate, the source of the respective ions should not contain ions which would adversely affect formation of the desired complex ion or adversely affect the oxidation-reduction reaction necessary for image amplification. Preferably, the selection of such ion sources should not result in precipitate formation between the negative ion of the metal ion source and positive ion for the complexing acid ion source. Thus, the salt of complexing acid is preferably an alkali metal or ammonium salt both of which form soluble salts with most negative ions.

In summary, the sources of the various metal ions and complexing ions, respectively, as well as the solutions thereof used in the foregoing processes should contain only ions which are photographically acceptable.

What is claimed is:

1. Process of amplifying a latent metal image of a' photographic copy medium said image being capable of initiating deposition of copper metal when contacted with a physical developer comprising a solution of copper ions,

and which comprises contacting said medium with a solution of copper ions and contacting the medium with a reducing agent selected from the group consisting of vanadous ion, titanous ion and complexes of vanadous, ti tanous or ferrous ion with a complexing organic carboxylic acid containing at least one amino nitrogen and at least two carboxyl groups, said carboxyl groups being separated from said amino nitrogen by at least one methylene r methine group.

2. Process as in claim 1 wherein the photographic medium comprises a photoconductor.

3. Process as in claim 1 wherein the photographic medium comprises a photosensitive silver halide.

4. Process as in claim 1 wherein the complexing acid is ethylenediaminetetraacetic acid or nitrilotriacetic acid.

5. Process as n claim 1 wherein the said complex is a complex of titanous ion with ethylenediaminetetraacetic acid or with nitrilotriacetic acid.

6. Process as in claim 1 wherein the copper ion comprises copper (II).

7. Process as in claim 1 wherein the copper ion comprises copper (I).

8. Process as in claim 7 wherein copper (I) is a com plex ion of copper (I) with chloride ion, sulfite ion or ammonia.

9. Process as in claim 7 wherein the source of copper (II) is cupric sulfate, cupric nitrate or cupric acetate.

10. Process as in claim 9 wherein the reducing agent is titanous or ferrous ethylenediaminetetraacetic acid or titanous nitriloacetic acid.

11. Process as in claim 1 wherein thiourea is present during the reduction of copper.

12. Process as in claim 1 wherein the copper ion is in the form of cupric ethylenediaminetetraacetic acid or cupric nitrilotriacetic acid and the reducing agent is titanous ethylenedaminetetraacetic acid or titanous nitrilotriacetic acid.

13. Process as in claim 1 wherein the metal of said latent image is silver, gold, copper, palladium or tin.

14. Process of producing a visible image on an imagewise exposed photographic medium comprising a radiation activatable photoconductor which comprises sensitizing said medium with a solution of copper ions and contacting the sensitized medium with a reducing agent selected from the group consisting of vanadous ion, titanous ion and complexes of vanadous, titanous or ferrous ion with a complexing organic carboxylic acid containing at least one amino nitrogen and at least two carboxyl groups, said carboxyl groups being separated from said amino nitrogen by at least one methylene or methine group.

15. Process as in claim 14 wherein the complexing acid is ethylenediaminetetraacetic acid or nitrilotriacetic acid.

16. Process as in claim 14 wherein the said complex is a complex of titanous ion with ethylenediaminetetraacetic acid or with nitrilotriacetic acid.

17. Process as in claim 14 wherein the reducing agent is selected from the group consisting of ferrous ethylenediaminetetraacetic acid, titanous ethylenediaminetetraacetic acid and titanous nitrilotriacetic acid.

18. Process as 11 claim 14 wherein the copper ion comprises copper (II).

19. Process as in claim 14 wherein the copper ion comprises copper (I).

20. Process as in claim 14- wherein the copper (I) is a complex ion of copper (I) with chloride ion, sulfite ion or ammonia.

21. Process as in claim 14 wherein the source of cop per (II) is cupric sulfate, cupric nitrate or cupric acetate.

22. Process as in claim 14 wherein thiourea is present during the reduction of copper.

23. A photographic copy medium comprising a photoconductor as photosensitive component thereof and a photographic reducing agent selected from the group consisting of vanadous ion, titanous ion, and complexes of titanous, vanadous or ferrous ion with a complexing organic acid containing at least two carboxyl groups and an amino nitrogen which is separated from the carboxyl groups by at least one methylene or methine group.

24. Medium as in claim 23 including a source of copper ions.

25. Medium as in claim 24 wherein the copper ion source is cupric nitrilotriacetic acid or cupric ethylenediaminetetraacetic acid and the reducing agent is titanous nitrilotriacetic acid or titauous ethylenediaminetetraacetic acid.

26. Medium as in claim 23 wherein the photoconductor is titanium dioxide.

27. Medium as in claim 26 wherein the titanium dioxide is contained in a layer comprising a binder therefore on a flexible support.

References Cited UNITED STATES PATENTS 2,891,871 6/1959 Ccresa 117130 3,403,035 9/1968 Schneble et a1. 1l7l30 3,152,903 10/1964 Shepard et a1. 96-60 3,256,092 6/1966 Means et al 9660 3,458,316 7/1969 Viro 9694 FOREIGN PATENTS 1,064,725 4/ 1967 Great Britain.

285,447 3/1965 Australia 96-48 PD NORMAN G. TORCHIN, Primary Examiner 

